Thermal design of dual circulating fluidized bed reactors for a large-scale CO₂ capture system

A dual circulating fluidized bed reactor has been studied for carbon dioxide (CO₂) capture. It is important to maintain the reaction temperature of the adsorbent in the carbonation–regeneration cycle. The dual circulating fluidized bed reactor will be used ultimately in the large reactors of industrial-sized power plants to control CO₂ emissions. However, to date, studies have considered only small-scale reactor models, due to the limitations associated with two-phase flow dynamics and changes in the heat transfer characteristics with reactor size. In this study, we investigated the thermal design of a feasible pilot-scale reactor through thermal-fluid analysis of the reactor and heat transfer in two-phase flow. Based on our thermal-fluid experimental results for a laboratory-scale dual circulating fluidized bed reactor with an amine-functionalized silica sorbent 0.37EB-PEI, a thermal design process was carried out to increase the reactor scale. In consideration of the heat of reaction and the sensible heat for a continuous process, the increase in total heat duty at the reactor scale has been determined. In the overall heat transfer process of the reactor, consisting of three heat transfer mechanisms, the bed-to-wall heat transfer by gas-solid fluidization was identified as the dominant mechanism. The scale-up of the fluidized bed resulted in a change in gas-solid behaviors and a lower heat transfer coefficient. Ultimately, through the thermal design process, the heat exchange area required for a large-scale carbonation reactor and regeneration reactor were derived; specifically, for the pilot-scale reactor to accommodate > 2000 m³/h flue gas, the required reactor height was estimated to be about two times compared to not taking the scale-up effect into account. We proposed a multi-tube reactor with the high heat transfer coefficient and the large heat transfer area for an efficient large-scale CO₂ capture system.